Drive control system for sensor-less motor

ABSTRACT

A drive control system, with PLL control, drives a rotatable multi-phase sensor-less motor by switching a current of a field coil of each phase depending on the rotating phase of the motor. When the moto is driven, a desired phase is selected as a datection phase, and a voltage induced on the coil of the detection phase is detected when power is fed for a predetermined time to the field coils other than the detection phase. A magnetic pole position is detected from the amplitude condition of the detected induced voltage. Based on this detection, the power-feeding phase of the motor drive is determined. Power feeding and pole position detection are performed alternately.

BACKGROUND OF THE INVENTION

The present invention relates to a drive control system for sensor-lessmotor and more specifically to the technique which may effectively beapplied to the drive control of a brush-less DC multi-phase motor notincluding a rotation detecting sensor, for example, the technique whichcan be effectively applied to the drive control of a spindle motor forhigh speed drive of a disk storage medium (platter) of a HDD (hard diskdrive)

The HDD reads or writes information with the seeking and followingoperations of a magnetic head on a recording surface formed on thesurface of platter while the disk type magnetic recording medium calledthe platter is rotated at a high speed. In order to realize high speedread/write operations of information in this HDD, the rotating speed ofplatter must be increased.

The platter is driven to rotate with a spindle motor. For this spindlemotor, a sensor-less motor is generally used. This sensor-less motor isa brush-less DC multi-phase motor not including a rotation detectingsensor. This motor is suitable, for example, for high speed rotation ofa disk type recording medium such as a platter.

The sensor-less motor can form an effective structure of the motor anddrive system thereof since an independent rotation sensor is not used todetect the magnetic pole position of a rotor. Instead, the magnetic poleposition of rotor must be detected without use of the sensor. Therefore,the magnetic pole position of rotor is detected, in the sensor-lessmotor of this type, by utilizing B-EMF (Back Electromagnetic Force)induced on a field coil. B-EMF is a voltage induced on the field coilthrough the rotation of a rotor. Therefore, when the rotor is in therotating condition, the magnetic pole position of rotor and rotatingspeed can be detected by utilizing its B-EMF.

In the case where this sensor-less motor is used as the spindle motor,the motor is driven to rotate with an open loop control and issequentially subjected to the commutation control and PLL (phase lockloop) control based on the back electromotive force of the field coil inview of holding the motor in the predetermined steady rotating speedcondition. The sequence control up to the steady operation from thisdrive can be conducted with an LSI (semiconductor integrated circuit)system.

SUMMARY OF THE INVENTION

However, the inventors of the present invention have found the techniqueexplained above has following problems.

In other words, in the drive control of a sensor-less motor explainedabove, the drive control in the steady rotating condition can berealized rather easily with the commutation and PLL controls based onthe back electromotive force of field coil, but detection of rotationwith the back electromotive force cannot be utilized during thetransitional condition until the steady rotating condition is started,particularly immediately after the drive. Therefore, the drive controlat the time of starting the motor is executed with the open loop controland when the rotation reaches a certain rotating speed with the openloop control, such open loop control is shifted to the communication andPLL controls. However, since the open loop control is a kind ofestimated control method and the estimated operation cannot always beattained. In the prior art, it has been inevitable that a fault isgenerated at the beginning of drive with a certain probability.

In the sensor-less motor not including a rotation sensor, if a drivemistake occurs, it is difficult to accurately detect such mistake. Adrive mistake occurs when the estimated operations are not carried outwith a certain reason. Therefore, if a drive error occurs, detection ofsuch drive mistake is not executed as estimated with a considerableprobability. In this case, various problems such that recovery from thedrive error and re-drive are delayed or the motor is stacked in thenon-driven condition may be generated.

Moreover, a problem that shift to the steady operation from drive is notcarried out smoothly and the sequence to shift to the drive control ofsteady operation is executed even when the drive fails has beengenerated easily.

When the motor is driven successfully and the drive control is shiftedto the PLL control, the phase lock of the PLL control is unlocked in acertain case, for example, when a load of motor changes to a largeextent. In this case, the motor is stepped out or stops in the worstcase. The motor of this type is driven with the PWM-controlled currentbut when the motor is stepped out, a regeneration current in the PWMdrive is returned to the power supply and thereby the power supplyvoltage rises irregularly, resulting in the possibility of breakdown ofthe drive circuit.

Loss of synchronization (step-out) due to the unlock of PLL is alsogenerated in some cases when the PWM duty becomes 100% due to reductionof voltage and over-load condition. A spindle motor is subjected to thesoft-switch drive or sine-wave drive for smoothly changing over thepower feeding phase. In this case, when the PWM duty reaches 100%, acurrent of the non-power feeding phase cannot be perfectly reduced tozero at the timing near the timing for detecting zero-cross of B-EMF andthereby a kick-back is generated in the drive voltage. Therefore, whenthe rotating position of rotor is detected with the zero-cross phase ofB-EMF, such kick-back prevents accurate detection of the zero-crossphase and thereby such detection error becomes large and PLL isunlocked.

The first object of the present invention is to provide technique foraccurately and quickly driving the sensor-less motor.

The second object of the present invention is to provide the techniquefor accurately monitoring the conditions of the sensor-less motor at thetime of drive in order to quickly drive the sensor-less motor withhigher reliability.

The third object of the present invention is to provide the techniquefor quickly realize recovery from a drive mistake and re-drive of motoreven when a drive mistake occurs in the sensor-less motor.

The fourth object of the present invention is to provide the techniquefor quickly realize recovery from a fault condition by accuratelydetecting unlock of the PLL when the sensor-less motor is successfullydriven and shifted to the PLL control condition.

The fifth object of the present invention is to provide the techniquefor accurately detecting the rotating position of rotor with zero-crossof B-EMF.

The aforementioned and the other objects and features of the presentinvention will become apparent from the following explanation of thisspecification to be made with reference to the accompanying drawings.

The typical inventions of the present invention disclosed in thisspecification can be explained briefly as follows.

The present invention discloses a drive control system for sensor-lessmotor in which the motor is driven to rotate by switching a current of afield coil in each phase of a multi-phase sensor-less motor depending onthe rotation phase of motor and the drive control thereof is subjectedto the PLL control. Moreover, immediately after the drive of motor, adesired phase is selected as the detection phase, a voltage induced onthe coil of the detection phase when the power is fed only for a shortperiod of time to the field coil in the phase other than the detectionphase and the magnetic pole position of rotor is detected from theamplitude condition of the induced voltage detected. Based on thisdetection, the power feeding phase of motor drive is determined and thepower feeding to drive the motor is conducted depending on suchdetermination. The detection of magnetic pole position and the powerfeeding to drive the motor are conducted alternately. Accordingly, driveof sensor-less motor can be realized accurately and quickly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram illustrating the drive controlsystem for sensor-less motor to which the present invention is applied.

FIG. 2 is a system structural diagram particularly illustrating a partfor drive control of motor in the drive control system for sensor-lessmotor of the present invention.

FIG. 3 is a timing chart illustrating schematic magnetic pole positiondetecting operation performed when the motor is driven.

FIG. 4 is a flowchart illustrating the procedures of detection ofmagnetic pole position and determination of power feeding phase executedin the first detection section.

FIG. 5 is a flowchart illustrating the procedures of detection ofmagnetic pole position and determination of power feeding phase executedin the second and subsequent detection sections.

FIG. 6 is a flowchart illustrating the procedures of offset accumulationprocess.

FIG. 7 is a flowchart illustrating the procedures of sense resultaccumulation process.

FIG. 8 is a truth value table illustrating variable conditions of thepower feeding phase and sense phase when an induced voltage is detectednormally.

FIG. 9 is a truth value table illustrating variable conditions of thepower feeding phase and sense phase when a part of the induced voltageis unclear.

FIG. 10 is a truth value table illustrating variable conditions of thepower feeding phase and sense phase when a larger part of the inducedvoltage is unclear.

FIG. 11 is a flowchart illustrating procedures up to the steady rotationfrom the drive of motor.

FIGS. 12(a) and 12(b) are waveform-charts illustrated the process todetect unlocking of the PLL control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be explainedwith reference to the accompanying drawings.

FIG. 1 schematically illustrates the drive control system forsensor-less motor to which the technique of the present invention isapplied. The system illustrated in this figure is integrally formed onsingle semiconductor substrate using single crystalline silicon, exceptfor the field coils Lu, Lv, Lw of motor. Moreover, the systemillustrated in the same figure is formed of an analog signal processingpart (within the frame of broken line A) and a digital signal processingpart (outside of the frame of broken line A). Both circuit portions maybe integrated on the single semiconductor substrate or formed separatelyon different semiconductor substrates as required. In regard to thedigital signal processing part, a part or entire part of the functionmay be formed with a software using a microcomputer.

In FIG. 1, a sensor-less motor as the control object is of the 3-phasesystem, including the field coils Lu, Lv, Lw in each phase. One ends ofthe field coils Lu, Lv, Lw of each phase are respectively connected tothe analog signal processing part via external terminals. Moreover, theother ends of the field coils Lu, Lv, Lw of each phase are connected incommon. The analog signal processing part (within the frame of brokenline A) is formed of a motor drive current output circuit 11, a coilvoltage detection amplifier 16 and a motor current detection amplifier13, etc.

The drive current output circuit 11 supplies a 3-phase drive current tothe field coils Lu, Lv, Lw of a 3-phase brush-less motor. The coilvoltage detection amplifier 16 detects a back electromotive force or aninduced voltage generated on the motor coils Lu, Lv, Lw. The motorcurrent detection amplifier 13 preliminarily amplifies a detectedvoltage of a current (motor current) flowing into the motor coils Lu,Lv, Lw. The motor current is detected through voltage conversion with acurrent detection resistor inserted in series to the current feedingpath of motor. The current detection resistor (RNF) is externallyconnected via an external terminal. The current detection amplifier 13preliminarily amplifies a current detection voltage divided to thecurrent detection resistor up to the predetermined level.

The digital signal processing part (outside of frame of the broken lineA) comprises an A/D converter (ADC) 14, a PWM pulse generator 20, a DCO(Digital Control Oscillator) 24, a phase difference detector 22, a powerfeeding phase control circuit 25, a motor rotation control part 32, asequencer 30, a serial input/output port 29, a soft-switch register 38,a power feeding phase control register 40, a drive current controlregister 42, a magnetic pole position detection control register 44 andan arithmetic block 46. Respective portions (20, 22, 24, 25, 29, 30, 32,38 to 46) are mutually connected with the common bus.

The A/D converter 14 switches for digital conversion a motor currentdetection voltage preliminarily amplified by the current detectionamplifier 13 and a back electromotive force or induced voltagepreliminarily amplified by the coil voltage detection amplifier 16. ThePWM pulse generator 20 PWM-controls a drive current of motor. The DCO 24generates the reference clock for the PWM control and power feedingphase control. Operation mode of this DCO 24 can be variably set withthe soft-switch register 38, power feeding phase control resistor 40,drive current control register 42 and magnetic pole position detectioncontrol register 44.

The phase difference detector 22 detects a phase difference between thezero-cross point of the back electromotive force and the zero-crosspoint of the drive current of each phase of motor. The power feedingphase control circuit 25 executes phase control of the motor drivecurrent by detecting the magnetic pole position of rotor. The motorrotation control part 32 judges the rotating speed at the time ofdriving the motor and shifts to the acceleration mode with the initialdrive when the motor is rotating in the lower speed or stops therotation, while executes the control such as acceleration with the PLLcontrol when the rotating speed of motor increases to a certain degree.

The sequencer 30 executes the control procedures such as drive andre-drive of motor. In practical, the sequencer 30 controls theoperations such as magnetic pole position detection control, powerfeeding phase control, drive current control and soft-switch controlwhich will be explained later. The serial input/output port 29 exchangescontrol data (DATA) for external side. The arithmetic block 46 usesregisters 38 to 44 to form a main control part for centralizedmanagement and control of the operating conditions in the system.

The system explained above forms the function block for the magneticpole position detection control, power feeding phase control, drivecurrent control, soft-switch control and drive sequence control. Detailsof these controls will be explained with reference to FIG. 2.

FIG. 2 illustrates a system structural diagram focusing on the partparticularly in regard to the drive control of motor among the drivecontrol system for sensor-less motor of the present invention.

In the same figure, the magnetic pole position detection control blockdetects the magnetic pole position of rotor by utilizing amplitudechange of the induced voltage (Eu, Ev, Ew) generated when the power isfed for a short period of time to the motor coils Lu, Lv, Lw. When thepower is fed for a short period of time to any one or two of the motorcoils Lu, Lv, Lw, the mutual inductance among the coils Lu, Lv, Lw ismodulated with the magnetic saturation phenomenon depending on themagnetic pole position. Accordingly, amplitude of the induced voltage(Eu, Ev, Ew) generated on the coil of non-power feeding phase changes.Based on this changing condition, the magnetic pole position isdetected. In this case, the power feeding is conducted with a shortpulse current with which the rotor does not react. Consequently, evenwhen the motor is in the stop condition or is rotating at a lower speedand the magnetic pole position cannot be detected based on B-EMF, themagnetic pole position can be detected.

The induced voltage (Eu, Ev, Ew) of the motor coils Lu, Lv, Lw isinputted to the A/D converter 14 via the selector 17, coil voltagedetection amplifier 16, analog filter 18 and multiplexer 15. Thereby,the induced voltage is subjected to the digital conversion for eachcoil. In this embodiment, the A/D converter 14 includes a conversionrange of 10 bits and uses this range for the digital conversion of theinduced voltage of coil (Eu, Ev, Ew) or back electromotive force (Vu,Vv, Vw) and moreover for digital conversion of the motor currentdetection voltage which is preliminarily amplified with the currentdetection amplifier 13. Therefore, in the analog input side of the A/Dconverter 14, the multiplexer 15 is provided for inputting two analoginputs through the switching process.

The power feeding phase control block performs, in the power feedingphase control circuit 25, the control for determining the power feedingphase of the motor drive current based on the back electromotive force(Vu, Vv, Vw) and the initial acceleration sequence control of motorbased on the magnetic pole position detection. To this power feedingcontrol circuit 25 to execute this control, a digital conversion output(ADCOUT) of an induced voltage (Eu, Ev, Ew) and a back electromotiveforce (Vu, Vv, Vw) is inputted.

While the motor is rotating at the speed higher than the predeterminedspeed, B-EMF (Vu, Vv, Vw) is generated due to the rotation in each coilLu, Lv, Lw. The zero-cross point of this B-EMF is detected with acomparator (zero-cross comparator) 19. A phase difference between thiszero-crosspoint and motor power feeding timing is detected with a phasedifference detector 22. This detection output is sent to a filter 23 andis then inputted to the DC024 as an oscillation frequency control signal(fdco). The filter 23 is provided to enhance an S/N ratio of detectionand an influence of high frequency noise can be eliminated by conductingthe averaging process through accumulation an error detection output.

An oscillation output (fcom) of the DC024 is inputted to a power feedingswitching control circuit 21 as the reference clock (CLK) of powerfeeding control. The power feeding switching control circuit 21 executesthe switching of phase (commutation) of the motor drive current based onthe reference clock (CLK).

A drive current control block compares the digital-converted motorcurrent detection signal (ADCOUT) with the motor current control signal(SPNCRNT DATA) given externally via the serial input/output port 29 forPWM-control of the motor drive current to make zero an error betweenboth signals. In this case, an error of these signals is detected withan error current detector 27. The detected error is accumulated in afilter 28 to compensate for stability of current control loop and isthen averaged. Thereafter, the average error signal is applied to a PWMpulse generator 20 as a control signal for determination of duty. ThePWM pulse generator 20 determines, based on above error, an amplitude ofthe drive current to be applied to the motor coils Lu, Lv, Lw, namelythe duty. Accordingly, the duty of motor drive current outputted fromthe current output circuit 11 is controlled for the feedback.

A motor current detection signal can be obtained by sampling a currentdetection voltage divided for both ends of a current detection resistorRNF provided in series to a common feeding path of the motor current(ISPN) with a sampling-hold circuit 12 and then amplifying the currentdetection voltage with an current detection amplifier 13. This amplifiedoutput (CRNTOUT) is digital-converted with the A/D converter 14.

A soft switch control block smoothly switches the power feeding phaseusing a soft switch control circuit 26. The soft switch control circuit26 generates, with arithmetic operation, an application voltage waveforminformation for the motor drive current output circuit 11 depending onthe detection value of current flowing into the coil. The power feedingphase can be switched smoothly by controlling an output waveform of themotor drive current output circuit 11 with the waveform generatedthrough arithmetic operation. Moreover, in this control block, a phasecontrol signal (fcom) indicating the magnetic pole position and acurrent control signal (ADCOUT) indicating the drive current are fedback to conduct the control to compensate for the power feeding phase toalways generate a higher torque without relation to variation of thedrive current.

A drive sequence control block determines the drive sequence of motor bycontrolling each control block of the magnetic pole position detectioncontrol, commutation control, drive current control and soft switchcontrol. Operations of this control block is performed with thesequencer 30 illustrated in the figure.

FIG. 3 is a timing chart illustrating schematic magnetic pole positiondetecting operation conducted when the motor is driven. The operationillustrated in this figure is executed based on the logic condition ofthe first and second status signals (COMSENS) and (PHASE). The periodwhere the first status signal (COMSENS) is in the High level indicatesthe initial drive control section of motor to conduct the magnetic poleposition detection control explained above. In this initial drivecontrol section, namely in the period where the first status signal isin the High level, the second status signal (PHASE) alternately repeatsthe High and Low levels.

In the period where the second status signal (PHASE) is in the Highlevel, the detecting section (SENS1 or SENS2) for determining the powerfeeding phase through the detection of magnetic pole position is set.Moreover, in the period where the second status signal (PHASE) becomesLow level, the power feeding is conducted to the determined phase forthe predetermined period to set the drive section (DRIVE) foraccelerating the motor. Namely, detection of magnetic pole position andinitial drive of motor are alternately repeated. This condition can bemonitored from the external side by externally reading the logiccondition of the status signal (PHASE).

The detection section (SENS1) which is set first in the initial drivecontrol section is composed of the phase U sense period, phase V senseperiod and phase W sense period and the initial value of the magneticpole position of rotor is detected by sensing all phases. In this senseoperation, any one of the 3-phase motor coils LUu, Lv, Lw is defined asthe sense phase and the remaining two motor coils are defined as thepower feeding phase (excitation phase). The power is fed for a shortperiod of time to the two motor coils in the power feeding phase and aninduced voltage appearing on the motor coil of the non-power feedingphase is detected. For example, in the phase U sense period, the poweris fed to the motor coils of phases V and W and an induced voltage ofthe coil of the phase U is detected. In the first detection period(SENS1) of the initial drive control, the sense operation is performedfor three phases of U, V and W.

Each sense period is respectively composed of a high impedance outputsection (Hi-Z) for ceasing excitation of motor coil, an offsetaccumulation section (offset) for accumulating back electromotive force(B-EMF) and offset of circuit under the same condition and a senseaccumulation section for accumulating voltage appearing in thenon-voltage feeding phase (sense phase) through excitation with feedingof power to the phase other than the sense phase. Since the voltagesignal measured in the sense accumulation section includes the backelectromotive force (B-EMF) and circuit offset, only the true inducedvoltage element appearing in the non-power feeding phase is obtained bysubtracting the value measured in the offset accumulation section(offset) from the measured value of the sense accumulation section.

With the sense operation for all phases in the first detection section(SENS1), the magnetic pole position of rotor is detected. The powerfeeding (excitation) is performed in the subsequent drive section(DRIVE) to generate a forward torque from the detected magnetic poleposition. In the detection section to be set after the drive section(DRIVE), namely the second and subsequent detection section (SENS2), thesense operation is performed only for the relevant one phase under theassumption that the motor is forward-driven with the drive section(DRIVE) before this detection section and the phase for power feeding(excitation) in the next drive section (DRIVE) is determined based onthe result of sense operation explained above.

As explained above, even if the rotor is not in the rotating conditionor in the rotating condition in the too lower speed to detect themagnetic pole position with the back electromotive force, the magneticpole position of rotor can be detected. Therefore, the motor can also bedriven by feeding the power for drive after determining the phase to bedriven based on such detection of magnetic pole position of rotor. Ifthe motor is not driven in the first drive section, the motor can bedriven with very high probability by alternately repeating, as explainedabove, the detection section and drive section.

FIGS. 4 to 7 illustrate flowcharts of the sequence of detection of themagnetic pole position and determination of power feeding phase. In thiscase, FIG. 4 illustrates the sequence of detection of the magnetic poleposition and determination of power feeding phase to be executed in thefirst detection section (SENS1). FIG. 5 illustrates the sequence ofdetection of the magnetic pole position and power feeding phase to beexecuted in the second (SENS2) and subsequent detection sections. FIG. 6illustrates the offset accumulation process sequence. FIG. 7 illustratesthe sense result accumulation process sequence.

The sequences of detection of magnetic pole position and determinationof power feeding phase to be executed in the first detection section(SENS1) executes first, as illustrated in FIG. 4, the offset measurementfor measuring and accumulating the offset values for the predeterminednumber of times in regard to the sense phases of U, V and W, sensemeasurement for measuring and accumulating an induced voltage for thepredetermined number of times, and calibration for measuring only thetrue induced voltage element by subtracting the measured and accumulatedvalue of offset from the measured and accumulated sense value (S41 toS43). Thereby, the sense values of the induced voltages for all threephases can be obtained (full-scan mode).

Next, whether all sense values are lower than the predeterminedthreshold value or not is judged for the sense values of all phases(S44) and whether the sense values of all phases are identical or not isalso judged (S45). When the magnetic pole position by sense of threephases is normally detected, a sense value of an induced voltage of anyone phase is always larger than the predetermined amplitude level(threshold value). Therefore, the magnetic pole position can betheoretically judged from the phase of which sense value indicates thelarger amplitude. Based on this result of judgment, the power feedingphase for driving the rotor to rotate in the specified direction (normalrotating direction) can be determined (S46). Amplitude of the sensevalue is determined by the two-level judgment of High and Low level.

When all sense values of induced voltages of three phases are amplitudesless than the predetermined level when the sense is completed, themagnetic pole position cannot be judged. In this case, the sense isassumed to be failed and a fault flag COMFAIL is set (S47).

Moreover, even if the sense values of induced voltages of three phasesare higher than the predetermined level, when the sense values are allidentical, the magnetic pole position cannot be judged. Accordingly, inthis case, a fault end flag COMFAIL is also set (S48).

As explained above, in the detection of magnetic pole position, it canbe known with the fault end flag COMFAIL that detection of magnetic poleposition is failed. Therefore, measures such as re-setting of detectedparameter (sense accumulation time) and displacement of initial positiondue to the control for power feeding phase of open loop can be executedquickly by monitoring the condition of flag COMFAIL. Accordingly,reliability for drive of motor can be enhanced.

Detection of magnetic pole position explained above is realized byutilizing the fact that when the power is fed for a short period of timeto the motor coil, amplitude of the voltage induced by the mutualinduction effect in the non-power feeding phase changes depending on themagnetic pole position of the rotor. In this embodiment, it is utilizedthat the induced voltage changes depending on the magnetic saturationcharacteristic of the mutual inductance of coil.

Sequence of detection of magnetic pole position and determination ofpower feeding phase to be executed in the second section and subsequencesections (SENS2) is executed in the single sense motor to sense only onepredetermined phase as illustrated in FIG. 5. At the time of initiallydriving the motor, the full-scan SENS1 must be executed because themagnetic pole position of motor is uncertain, but when the power feedingphase is once determined, the phase to be switched next can be uniquelydetermined. Therefore, the desired phase switching position can bedetermined by sensing only one phase in the magnetic pole positiondetection.

In FIG. 5, whether power feeding for drive to be executed afterdetection of magnetic pole position is conducted exceeding the specifiednumber of times or not. When less than the specified number of times,the power feeding for drive is conducted to the power feeding phasedetermined on the basis of the preceding detection of magnetic poleposition (S51, S52).

After power feeding for drive, an accumulation register for measurementis reset and only one sense phase for measuring an induced voltage isdetermined (S53, S54). The sense phase can be determined uniquely fromthe result of the preceding detection of magnetic pole position.

The offset measurement for accumulating the offset values by conductingmeasurement for the predetermined number of times is executed for themotor coil of the determined sense phase (S55). Next, the sensemeasurement for accumulating the induced voltages for the predeterminednumber of times is conducted and calibration is also conducted bymeasuring only the true induced voltage element by subtracting themeasured and accumulated value of offsets from the measured andaccumulated value of sense (S56). When the motor rotates to generate aback electromotive force, only the induced voltage after subtraction ofthe back electromotive force can be measured by executing calibration.

Thereafter, whether the fault end flag COMFAIL is set or not is judgedby comparing the induced voltage sense values of three phases. In thisdetection section (SENS2), only the induced voltage of one phasedetermined depending on the result of preceding detection of magneticpole position is sensed. Therefore, the sense values of the other twophases as the comparison object use the result of measurement in thepreceding detection of the magnetic pole position.

When the sense values of induced voltages of three phases when the senseis completed are all amplitudes which are lower than the predeterminedlevel, the magnetic pole position cannot be judged. In this case, thesense is assumed to be failed and a fault end flag COMFAIL is set (S57,S59). Moreover, even when the sense values of induced voltages of threephases are higher than the predetermined level, if the sense values areall identical, the magnetic pole position cannot be judged. In thiscase, therefore, a fault end flag COMFAIL is set (S58, S60).

Since only the sense phase is considered in the second and subsequentsections (SENS2), the upper limit of rotating speed in the initial drivecan be raised by shortening the sense period. When the upper limit ofrotating speed in the initial drive is raised, a B-EMF generated in themotor becomes large to assure the initial drive and the shift to thesteady rotation by the PLL control can be realized smoothly. Moreover,since a ratio of the power feeding time to the sense time can beincreased, a merit that the upper limit of rotating speed can beattained within a shorter period of time can be obtained. In addition,since higher the rotating speed when the initial acceleration iscompleted, the higher the amplitude of back electromotive force (B-EMF)becomes, unlock due to the PLL control by detection of the backelectromotive force in the next step becomes difficult to occur andthereby reliability of drive can be enhanced.

In the offset accumulation sequence, as illustrated in FIG. 6, after theoffset accumulation register is initialized (reset), the digitalizedmeasured values are accumulated for the predetermined number of timesand are then stored in the offset accumulation register. Withaccumulation of the measured values, detection sensitivity and accuracymay be increased by reducing influence of high frequency noise andjitter or the like.

In the sense result accumulation process sequence, the forward powerfeeding is started for the coil of the relevant phase in order to detectan induced voltage (S71). Simultaneously, the first accumulationregister A is reset as the preparation for storing a new accumulatedvalue (S72). Under the forward power feeding condition, the measuredvalues detected from the coil of the non-power feeding phase andconverted to the digital values are then accumulated for thepredetermined number of times (S73). This accumulation result is storedin the first accumulation register A (S74).

Next, after the power feeding is paused for the predetermined time, thebackward power feeding is started for the coil of the relevant phase todetect an induced voltage (S75, S76). Simultaneously, the secondaccumulation register B is reset as preparation for storing a newaccumulated value (S77). Under the backward power feeding condition, themeasured values detected from the coil of non-power feeding phase andconverted to the digital values are accumulated for the predeterminednumber of times (S78). This accumulation result is stored in the secondaccumulation register B(S79).

A result of addition of contents of the second accumulation register Bto the first accumulation register A is stored to the first accumulationregister A(S80). Thereby, the accumulation results of induced voltagedetected respectively by the forward and backward power feedings areadded and polarity of induced voltage can be judged from the added sensevalue. Namely, whether the induced voltage has been amplified in theHigh level side, or in the Low level side or not amplified in the Highand Low level sides. When the amplitude is detected normally, the sensevalue may be judged as the High level or Low level. However, it is alsopossible that if a detection error is generated, the sense value is notjugged as normal/negative (H/L) level.

FIG. 8 to FIG. 10 illustrate the truth value table for the relationshipbetween the power feeding phase and sense phase when the motor isdriven. As explained previously, the detection of magnetic pole positionand power feeding for drive are alternately conducted when the motor isdriven to rotate, but second and subsequent detections of magnetic poleposition may be conducted by detecting the induced voltage of any onephase. In this case, determination of sense phase can be set dependingon the predetermined logical rule as respectively illustrated in FIG. 8to FIG. 10. Namely, when the motor is driven to rotate in the constantdirection, polarity of induced voltages of U, V and W phasessequentially changes phase by phase depending on the preceding detectionresult of the magnetic pole position.

FIG. 8 illustrates changing conditions of the power feeding phase andsense phase (phase detected after power feeding) when the inducedvoltage is normally detected in any polarity of the positive/negative(H/L) polarities. In this case, first, the power feeding phase isdetermined based on the preceding detection result of the inducedvoltage and the power feeding for drive is conducted in this determinedpower feeding phase. After the power feeding for drive, the sense phaseis determined for detection of induced voltage. In this case, thedetection phase can be determined based on the just preceding powerfeeding phase.

For example, when the detection result of induced voltage of each phasedetected in the preceding detection of magnetic pole position is phaseU=L, phase V=L, and phase W=H, the drive power feeding phase determinedbased on this detection result becomes phase U=L (sink), phase V=H(source), and phase W=off. In this case, detection of induced voltageafter the power feeding for drive is executed for the phase U becausethe phase of which polarity of induced voltage changes next can beassumed as the phase U.

When the power feeding for drive is executed at the magnetic poleposition where the induced voltage becomes L for the phase U, L for thephase V and H for the phase W, the polarity changes only in the phase Uand polarity change of induced voltage does not occur in the phases Vand W. Therefore, in this case, it is enough that whether polaritychanges as assumed or not is judged by detecting only the inducedvoltage of phase U. As explained above, when only one phase of inducedvoltage is detected after the power feeding for drive, the power feedingphase and detection phase can be determined alternately.

However, detection of induced voltage is not always executedsuccessfully. For example, in an example of FIG. 7, even when therising/falling waveform of the induced voltage is ideal waveform,detected polarity of induced voltage cannot be judged as H or L in somecases because the transitional rising/falling waveform is destroyedactually if the detected sensitivity is insufficient.

For example, as illustrated in FIG. 9, the rising/falling condition ofinduced voltage is ambiguous and uncertain polarity (indicated by thesymbol X), neither H nor L, of the induced voltage is detected at thearea near the rising/falling edge. However, even in this case, the powerfeeding phase and detection phase may be uniquely and theoreticallyjudged based on the preceding processes. Moreover, the detection phaseof induced voltage after such power feeding can also be determined.

FIG. 10 illustrates the condition where ambiguous region of inducedvoltage is further expanded and the polarity of induced voltage becomesuncertain in the half of electrical angle of 360 degrees (−180 degreesto +180 degrees). Even in this case, the power feeding phase anddetection phase can also be judged uniquely and theoretically based onthe preceding processes.

The theoretical judgment explained above may be realized very easily andquickly by preparing the induced voltage detection pattern and timeseries change pattern of power feeding phase and detection phase in theshape of the logical table. Moreover, when contents of such logicaltable is not fixed, allowing write-setting by user using a programmablenon-volatile memory such as a flash memory, it is now possible for userto program as desired the setting of control condition, for example, tosuch degree ambiguity of polarity of induced voltage should be allowedor when to which degree ambiguity of polarity of induced voltage isexpanded, an error should be defined.

FIG. 11 illustrates a flowchart of sequence up to the steady rotationfrom drive of motor by the motor drive control system explained above.

In this figure, when a motor drive command is issued, the period ofB-EMF of coil is detected first to detect the rotating speed (rotatingfrequency) of motor (S201), considering issuance of motor drive commandafter the power failure occurs momentarily and such power failure isrecovered. This drive command is generated usually when the motor is inthe stop condition but is not always limited thereto.

Therefore, in the next step (S202), it is judged whether the rotatingspeed of motor is only a several percents (for example, 3%) of thetarget speed (Nt) or not in order to execute the steady rotation control(S203 to S207) with the PLL control or execute the drive sequence (S210to S215).

In the steady rotation control, rotation of motor is accelerated withthe power feeding phase control in the PLL control (S203). In this case,unlock of PLL is monitored (S204). Unlock of PLL can be judged, asexplained later, with the zero-cross timing of B-EMF. While the PLLcontrol is executed normally, a constant timing relationship ismaintained between the switching of power feeding phase and zero-crosspoint of B-EMF, but if the PLL control is no longer executed normally, afault is generated in such timing relationship. When unlock is judged asexplained above, a flag (ACCFAIL) indicating generation of fault is setand the process shifts to the predetermined fault process routine (S216)including the head drawing process or the like.

Moreover, when the motor rotating speed is higher, for example, 90% ofthe target speed, the motor is judged to reach the steady rotation, thesoft switch control is executed to assure smooth commutation of thepower feeding phase (S205, S206). The soft switch control makes smooththe commutation of power feeding phase and realizes low noise drive andlow torque ripple. Moreover, the soft switch also has a function tocompensate for the power feeding phase to always generate a highertorque, without relation to change of drive current, by feeding back thephase control signal (fcom) indicating the magnetic pole position andthe current control signal (ADCOUT) indicating the drive current as thecontrol information. If the phase control by the soft switch control isdisabled, the process returns to the step S201 for the repeated drive.

Meanwhile, when the motor is in the stop condition or is rotating in thetoo lower speed to realize acceleration by the PLL control, the drivesequence (S210 to S215) is executed. In this drive sequence, the initialacceleration (COMSENS) by detection of magnetic pole position isexecuted for the predetermined number of times (M times) (S210 to S212).In this case, every time when the initial acceleration is conductedonce, the process returns to the process routine (S201), it is checkedwhether the motor rotating speed has been accelerated with the initialacceleration up to the speed which may be accelerated with the PLLcontrol or not. Thereby, the initial acceleration can be completedwithout repletion of useless initial acceleration (COMSENS).

When the initial acceleration (COMSENS) fails (COMFAIL=1), followingrecovery processes are selectively executed. In one recovery process,since failure of initial acceleration is resulting from inadequateaccuracy of magnetic pole position detection, the parameter settingssuch as increase of current during detection and change of detectioninterval are changed (S214). Thereafter, the initial acceleration isexecuted again from the beginning. This process is selected when thenumber of times of re-trial process of initial acceleration process(S210 to S212) is less than the predetermined value (N) (S213).

When the number of times of re-trial process of the initial accelerationprocess (S210 to S212) has exceeded the predetermined number of times(N), since it is highly probable that the rotor stops at the position toeasily generate an magnetic pole position detection error, the rotor isdisplaced with the open loop control (S215). Thereafter, the initialacceleration is started again from the beginning.

In the control explained above, it is recommended that the target speed(Nt), upper limit in number of times of re-trial (N), and shiftingcondition and branching condition (for example, M) to and from the drivesequence (S210 to S215) are stored in a non-volatile memory such asflash memory for the user to desirably change the settings. Moreover,any one routine may be necessary for the steps S214 and S215 and it istherefore recommended to variably set these routines from external side.

In the sequence explained above, since the process returns to the firstroutine (S201) to check the success of the initial drive whenever theinitial drive is executed once, recovery from the fault condition may berealized quickly and adequately to improve the reliability of system.

FIGS. 12(a) and 12(b) illustrate waveform charts for explaining theprocess to set a fault judgment flag (ACCFALL=1) by detecting unlock ofthe PLL control in the drive sequence explained above. In this figures,CT indicatew the reference level of zero-cross detection.

In the same figures, when the PLL control is performed normally, theback electromotive force generated by rotation of motor indicateszero-cross within the switching period of the power feeding phasebecause the power feeding phase is switched based on the backelectromotive force. When the power feeding phase is switched normallyunder the PLL control, such zero-cross is performed within the switchingperiod at the power feeding phase. Switching of the power feeding phaseis performed in the detection period of the back electromotive force.

On the other hand, if the PLL control is no longer performed normally,the zero-cross point does not appear in the detection period of the backelectromotive force, namely in the switching period of the power feedingphase. Accordingly, in the acceleration mode due to the PLL control, amasking signal (MSK1 and MSK2) for detecting the zero-cross point onlywithin the switching period of the power feeding phase is generated andthe zero-cross point is detected in the period preset by this maskingsignal. Thereby, unlock condition of the PLL control is logically judgedand thereby the result (ACCFAIL) is outputted to the system.

The present invention has been explained practically based on thepreferred embodiments but the present invention is not limited to aboveembodiments and allows various changes or modifications withoutdeparture from the scope of the claims thereof.

For example, in the present invention, various parameters for detectionof magnetic pole position and determination of fault can be setlogically in variable but these parameters can be fixed previously atthe time of setting. For example, these parameters may be stored, asexplained above, to a non-volatile memory such as flash memory. In thiscase, it is recommended to introduce the structure that contents of thenon-volatile memory are externally updated and manipulated freely via aserial input/output port. Moreover, it is also possible that a pluralityof programs such as drive sequence are stocked in such non-volatilememory and a user can select the necessary program from these programsand then execute the selected program.

In above explanation, the present invention has been applied to thedrive control of the spindle motor of HDD which is the main applicationfield as the background thereof. However the present invention is notlimited there to and can also be applied, for example, to the drivecontrol of spindle motor such as the optical memory drive or opticalmagnetic memory.

The effects of the present invention may be briefly explained asfollows.

On the occasion of driving a multi-phase sensor-less motor, condition ofthe sensor-less motor at the time of drive can be detected accuratelyand even when drive error of sensor-less motor is generated, recoveryfrom drive error and re-drive of the motor can be performed quickly.Moreover, when the sensor-less motor is driven successfully and shiftsto the PLL control condition, unlock of the PLL is accurately detectedand can be recovered quickly from the fault condition. In addition, inthe case where the rotating position of rotor is detected with thezero-cross of B-EMF, detection of zero-cross can be performedaccurately. As a result, the sensor-less motor can be driven surely andquickly. Moreover, it is also possible that error may be detectedaccurately and process after generation of fault can be executed quicklyand adequately.

1. A drive control system for a multi-phase and sensor-less motor fordriving the motor by switching a current of a field coil in each phaseof the motor depending on a rotational phase of the motor, comprising: apower feeding circuit feeding electrical power, for a predeterminedperiod, to a selected field coil when the selected field coil is in aphase other than a detection phase to induce a voltage in another fieldcoil; an induced voltage detecting circuit detecting the induced voltageon said another field coil during the detection phase; a magnetic poleposition detecting circuit detecting a magnetic pole position of a rotorbased on an amplitude of said induced voltage; a driving circuitdetermining a power supply phase for drive of the motor based on themagnetic pole position, and executing power supply for drive dependingon the power supply phase; a control circuit alternately conductingdetection of the magnetic pole and power supply for drive of the motorby said driving circuit when a rotating speed of the motor is less thana predetermined speed; and a back electromotive force detecting circuitdetecting a back electromotive force on said field coil so as todetermine the power supply phase when the rotating speed of the motor isgreater than said predetermined speed, with drive of the motor beingexecuted based on a detection result of the back electromotive forcedetecting circuit.
 2. A drive control system according to claim 1,wherein the field coils of all phases undergo the detection phase duringa first period for detection of the magnetic pole position, the fieldcoil of only one phase is selected to undergo the detection phase in anext period for detection of the magnetic pole position.
 3. A drivecontrol system according to claim 1, further comprising a reset circuitprovided to reset detection parameters when said detection of themagnetic pole position fails and to re-try said detection of themagnetic pole position after said reset.
 4. A drive control systemaccording to claim 1, further comprising a rotor position controlcircuit provided to shift the rotor's position with an open loop controlwhen the detection of the magnetic pole position fails for apredetermined number of times, and to re-try said detection of themagnetic pole position after said open loop control.
 5. A drive controlsystem according to claim 1, wherein when conditions of the inducedvoltages detected in each phase are all identical or when amplitudes ofthe induced voltages detected in all phases are smaller than apredetermined threshold value, said detection of the magnetic poleposition is judged to have failed.
 6. A drive control system accordingto claim 1, wherein the detection of said induced voltage is executed byaccumulating a plurality of detected values obtained in a predetermineddetection period and condition of the induced voltage is judged using anaccumulated value generated by accumulating the plurality of detectedvalues.
 7. A drive control system according to claim 1, wherein acircuit is also provided to logically judge, when an amplitude of aninduced voltage obtained in any detection phase of said induced voltageis less than the threshold value, the magnetic pole position based on anormally detected induced voltage from a preceding magnetic poleposition detection.
 8. A drive control system according to claim 1,wherein prior to a detection of said induced voltage, an offset voltageis detected from the field coil to undergo the detection phase, and onlyan induced voltage component is detected in the detection phase bysubtracting a detected value of the offset voltage from a detected valueof the induced voltage.
 9. A drive control system according to claim 1,wherein said induced voltage is converted to a digital value, suchdigital conversion is executed a plurality of times for every detectionphase, and the results of the digital conversion are used as thedetected value.
 10. A drive control system according to claim 1, whereincondition setting parameters for a detection of the magnetic poleposition are stored in a programmable non-volatile memory, and contentsof the programmable non-volatile memory can be updated or manipulatedfrom an external side via a serial input/output port.
 11. The controllerof claim 1, further comprising a commutation circuit, and wherein theback electromotive force is a voltage induced on the another field coil.12. A motor controller comprising: a test power supply constructed toenergize a first coil of a plurality of coils in a motor with testpower; a detection circuit constructed to detect an induced voltagecaused by the test power supply on a second coil of the plurality ofcoils; a position determination circuit constructed to determine amagnetic pole position of the motor based on the induced voltage; adrive power supply constructed to supply drive power to the motor basedon the magnetic pole position when a rotational speed of the motor isless than a predetermined speed; a back electromotive force detectioncircuit constructed to detect a back electromotive force to control thedrive power to the motor when the rotational speed of the motor isgreater than said predetermined speed.
 13. The controller of claim 12,wherein the test power is a pulse current.
 14. The controller of claim12, wherein the test power is a pulse current insufficient to drive themotor.
 15. The controller of claim 12, wherein the positiondetermination circuit can detect the magnetic pole position when therotational speed of the motor is insufficient to detect the backelectromagnetic force.
 16. The controller of claim 12, wherein during astart-up period, the test power supply supplies test power to each coilof the plurality of coils in succession, and the induced voltage isdetected on another of the plurality of coils.
 17. The controller ofclaim 12, further comprising an open loop controller constructed torotate the motor in the event that the magnetic pole position cannot bedetected.
 18. The controller of claim 12, wherein the supply of thedrive power is alternated with detection of the magnetic pole position.19. The controller of claim 12, wherein the motor is a sensor-lessmulti-phase motor.
 20. A motor drive control system, comprising: athree-phase and sensor-less motor; a field coil; a magnetic poleposition detection unit that detects an amplitude of a voltage inducedin the field coil in a no power feeding phase based on a variation inmutual inductance while current is supplied to at least one other phaseof the motor, the magnetic pole position detection unit furtherdetecting the magnetic pole position based on the detected amplitude; acommutation Unit; a drive unit that, based on the magnetic poleposition, determines a drive phase in which a drive current to generatea torque of the motor is fed to the field coil; and a sequencer unitthat alternately executes a detection operation of the magnetic poleposition and a drive operation so that the drive current is supplied tothe field coil in the drive phase to execute an initial acceleration.21. A motor drive control system according to claim 20, wherein thesequencer unit is adapted to execute an initial acceleration operationincluding: detecting the magnetic pole position of the field coil in allphases so as to detect an initial value of the magnetic pole position,and detecting the magnetic pole position of the field coil in only onephase based on the initial value of the magnetic pole position.
 22. Amotor drive control system according to claim 20, wherein the sequencerunit resets detection parameters when said detection of the magneticpole position fails in order to re-try said detection of the magneticpole position after said reset.
 23. A motor drive control systemaccording to claim 20, wherein the sequencer unit executes a control toshift a rotor's position with an open loop control when the detection ofthe magnetic pole position fails for a predetermined number of times,and to re-try said detection of the magnetic pole position after saidopen loop control.
 24. A motor drive control system according to claim20, wherein when conditions of induced voltages detected in each phaseare all identical or when amplitudes of induced voltages detected in allphases are smaller than a predetermined threshold value, said detectionof the magnetic pole position is judged to have failed.
 25. A motordrive control system according to claim 20, wherein the detection of theamplitude of the voltage induced in the field coil includes integrationof a plurality of values obtained during a predetermined detectionphase.
 26. A motor drive control system according to claim 20, whereinwhen the amplitude of the voltage induced in the field coil obtained inany detection phase is less than a threshold value, the sequencer unitlogically judges the magnetic pole position based on a normally detectedinduced voltage from a preceding magnetic pole position detection.